Purification, crystallization and preliminary X-ray data collection of the N-terminal domain of the 26S proteasome regulatory subunit p27 and its complex with the ATPase domain of Rpt5 from Mus musculus

The protein 26S proteasome regulatory subunit p27 is one of the four chaperones that help in the assembly of the 19S regulatory particle (RP) of the 26S proteasome. In the present work, the N-terminus of p27 (residues 1-128) from Mus musculus was cloned, expressed, purified and crystallized alone and in complex with the C-terminal ATPase domain of Rpt5 (residues 173-442). The crystals of p27^(1-128) diffracted to 1.7 Å resolution and belonged to space group P2₁2₁2₁, with unit-cell parameters a = 26.79, b = 30.39, c = 145.06 Å. Resolution-dependent Matthews coefficient probability analysis suggested the presence of only one molecule per asymmetric unit, with 40.5% solvent content and a V_M value of 2.02 Å³ Da^-1. The crystal of the p27^(1-128)-Rpt5^(173-442) complex diffracted to 4 Å resolution and belonged to space group P222, with unit-cell parameters a = 75.93, b = 76.08, c = 336.85 Å. The presence of four heterodimers in the asymmetric unit with 53.2% solvent content and a V_M value of 2.63 Å³ Da^-1 or five heterodimers in the asymmetric unit with 41.5% solvent content and a V_M value of 2.10 Å³ Da^-1 is assumed.